Detection of past and recurrent marijuana use by a modified GC/MS procedure

A published gas chromatography/mass spectrometry method for detecting 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH) in urine was modified. In the new procedure, five GC/MS ion peaks of a pentafluoropropylpentafluoropropionyl derivative of THC-COOH are monitored in the multiple-ion mode for improved reliability; two ion peaks of the trideuterated internal standard are used for greater quantitative precision; and methanolic KOH is employed instead of NaOH in the hydrolysis and extraction steps to produce a cleaner extract. Finally, the new procedure is designed to keep THC-COOH either in basic solution or in an organic solvent at all times to prevent adsorption onto glass or plastic, so that disposable, non-silanized glassware may be used. Patient urines were analyzed by both the new procedure and the EMIT method. For 32 specimens, the average and range of EMIT/GC/MS concentration ratios were 2.8 and 0.9-7.2, respectively. Concentrations of THC-COOH measured by the GC/MS procedure may be more indicative of recent marijuana use than the EMIT semi-quantitative concentration values.